1. Field of the Invention
The present invention generally relates to an engine starter having an outstanding heat radiation or dissipation property.
2. Related Art
In a conventional starter such as shown in FIG. 4 and FIG. 5, a starter 100 is configured of a starter housing 102 fixed on a clutch housing 101, a pinion 103 for ring gear driving provided to freely rotate and freely slide in the axial direction within the starter housing 102, a starter motor 104 that drives the pinion 103 fixed in the starter housing 102, and a magnet switch 105. The starter housing 102 is configured of a pinion storage chamber S1, and a magnet switch drive lever storage chamber S2 for pinion drive. The opening of drive lever storage chamber S2 on the axial side opposite to pinion 103 is closed off by the starter motor 104 having a built-in planetary gear or epicycle gear speed reduction mechanism.
A pinion enclosing portion 102a of the starter housing 102 that encloses the pinion storage chamber S1 is fit into the clutch housing 101, and the installation surface 102a of the starter housing 102 directly contacts the installation surface 101s of the clutch housing 101.
In the conventional lever drive type starter, the installation surface 102s is arranged on the end of the pinion enclosure portion 102a, and only the pinion enclosure portion 102a of the starter housing 102 is fit into the clutch housing 101. Furthermore with the conventional starter, the axial length L1 of the pinion enclosure portion 102a from the axial end of the starter housing side fit into the clutch housing 101 to the starter installation surface 101s of the clutch housing 101 or starter housing installation surface 102 is set to be much shorter than the axial length L3 from the end of the starter housing side not fit into the clutch housing 101 to the starter installation surface 101s or starter housing installation surface 102s.
Furthermore, the exposed surface area of the portion of the starter housing 102 fit into the clutch housing 101 is set to be much smaller than the exposed surface area of the portion of the starter housing 102 not fit into the clutch housing 101 and of the starter motor 104.
On the other hand, a heat radiation or dissipation passage in the conventional starter motor is divided into the first passage that directly radiates the heat from the outer surface of the starter motor itself, the second passage that radiates the heat to the clutch housing via the installation surface, and the third passage that radiates the heat from the starter motor to the air in the clutch housing via the starter housing pinion enclosure portion.
However, high speed, compact size and large output are required recently in starter motors, due to the incorporation of epicycle reduction gear mechanism. As a result, the heat radiation has become a problem due to the increase in the heat generated at the motor portion. It thus become necessary to increase the exposed portion of the starter housing outside the clutch housing or the surface area of the starter motor to counteract to the increased heat radiation amount of the first passage. However, as the air flow rate or speed around the starter motor is extremely small when the engine is started, the heat transfer resistance is large. The temperature of the air near the starter motor rises when heated by the starter motor, an engine block or an exhaust pipe, and thus it is difficult to greatly increase the heat radiation amount even with the increase in the surface area. In particular, when the outside temperature is high and the surface temperature of the engine or the exhaust pipe near the starter motor is kept high immediately after the engine is stopped, the heat radiation amount at the first passage drops remarkably.
On the other hand, the increase in the surface area for the installation surfaces 101s and 102s of the starter housing and clutch housing, which mutually contact, can be considered for increasing the heat radiation amount in the second passage. However, due to the size and arrangement of other devices, in particular, drive transfer mechanism such as a transmission, it is not easy to increase the radius of the installation surfaces 101s and 102s. Furthermore, immediately after the engine is stopped, etc., the engine itself is hot, causing the clutch housing temperature to also rise. Thus, there are cases when the clutch housing cannot sufficiently absorb the heat generated when the starter motor is started.
In other words, requirement of high speed and high output to conventional starter motors is limited by severe outside air conditions for cooling, temperature and flow rate, at around the periphery of the starter motor.